Important Principles of Casting Safety

This article is about the Important Principles of Casting Safety. This is a very brief introduction to safety issues when casting in a small shop. It cannot hope to address the whole gamut of problems but can serve to introduce some important principles.

In general

Here’s something to aim for: a well laid-out, orderly workshop, well-lit by multiple non glare light sources, well-maintained equipment, electrically and fire safe, with low dust and few procedures involving solvents, with excellent local ventilation at the appropriate work stations (such as investing or melting areas), the use of work clothing, which is cleaned frequently, lots of personal safety equipment (earmuffs, shoe covers to protect against molten metal splashes, safety glasses etc.), different jobs and heights to work at over the work day, ergonomically considered working actions and a conscious attitude and consciousness of safety.

Choose procedures that don’t involve exposure to risks. Set things up so that you can’t hurt yourself. Make safety a habit and then it won’t seem like work. If you don’t use a certain chemical or hazardous procedure in your shop, then you are extremely unlikely to get hurt by it. Substitute less hazardous processes and materials for more dangerous ones. If you have an accident or a near miss it needs to be recorded in your accident book and discussed so as to avoid doing the same thing again.

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To escape unnecessary work, look for examples of people who have solved the same kinds of safety problems you have to solve, and see if you can adapt some of their ideas and approaches for your own small shop. Look for models around you.

There are some general points to mention before we list specific hazards of casting.

There are dusts you can see in the air. It is, however, the smaller, completely invisible particles that are the most dangerous. These, especially fibrous or jagged ones like asbestos, cotton and silica, are stored between the air sacs of the lungs. That is, you breathe them in and they will never escape again. Once there, they cause scarring, thickening of tissues, eventually stressing the heart because it is more work to breathe. Cristobalite (a rather vicious form of silica) exposure is considered a real silicosis hazard. It is a major component of casting investment.

Fumes are small particles of a material, often from metals that have been melted. These may be very tiny and can be breathed deeply into the lungs. Metal fume fever can be a real problem with molten metals. Metal fume fever can be caused by zinc, copper, magnesium, aluminum, copper, antimony, cadmium, iron and silver.

If you think you need a respirator to do something, red flags should be waving in front of your eyes and alarm bells ringing in your mind. If you have to use a respirator, there is something seriously wrong with your ventilation system and working processes. And when you take it off, whatever it was you were afraid of will still be there, an invisible dust (such as cristobalite investment) on all surfaces, so that merely walking past later will stir it up into the air so you can breathe it in. If you are using one, make sure it is correct for your face and for the dusts, chemicals and fumes you are protecting yourself from. Talk to your safety supply company representative, or better still several of them. It is easy to use the wrong respirator or to have an imperfect seal when you use it.

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Eye protection in the workshop usually consists of using safety glasses and/or a face shield. Polycarbonate glasses are good. Aside from protection from sharp objects, flying chunks, dust, chemicals, fumes, liquids and hot metal splashes, we have to deal with glowing materials (infrared light), the blue flame of a high-temperature torch (ultraviolet light) and “sodium glare or flare.”

Most glasses and polycarbonates will stop the ultraviolet. So will most contact lenses. The infrared is stopped by a “shade”: numbers 2 and up have been suggested. It is important that one understands that a “tinted” lens does not offer infrared protection-only a shaded lens offers protection. McCann notes that “most recent recommendations are to wear the darkest shade number consistent with being able to see your work (ANSI Z87.1-1989” (McCann, Artist Beware page 216). Side shields that stop UV and infrared are also a good idea. The sodium flare, which is more of a problem for glass workers, is stopped by didymium glasses.

Dilution ventilation is used in many shops, where you open a window next to you, and another one elsewhere, so that air passes you on its way out. Dilution ventilation is not generally an effective approach. What we really want most of the time is local ventilation, which means a sucking device, slot or tube very close to the working area that is generating the dust, mist or fumes so they are sucked away as they are produced: removed entirely from the workshop and vented safely (i.e. not near a makeup air intake).

Jewelers cast metals frequently, in making ingots for sheet and wire, sand casting, vacuum and centrifugal investment casting and so on. The investment burnout process normally occurs in kilns, and, depending upon the wax, or even plastic, used, the fumes can be from mildly toxic to extremely toxic, and in many cases are fairly polluting. Usually jewelers cast gold and silver alloys, sometimes other metals like platinum, brass, more rarely tin and zinc (white metals being spin cast) in the small workshop. Alloys may contain other metals which produce hazardous fumes such as lead, cadmium, beryllium, arsenic and antimony. Nickel, too is considered a suspect metal now. Manganese and chromium are also to be avoided. Casting involves heat and its dangers of burns, damaging infrared and ultraviolet light (radiation).

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The preparations for casting involve wax working, solvent exposure, tool use, mold making (boy those scalpels are sharp), injection, and other jobs which are not dealt with here, nor are the issues of de-vesting and finishing castings. In this article investing, burnout and casting metals are discussed.

Casting hazards in general can be divided into certain types.

Chemical: By inhalation, ingestion and skin contact. Don’t eat, drink, smoke, bite your nails or apply makeup in the workshop as a matter of principle. Smoking, besides being bad for you in all the ways you ought to know about by now, seems to react synergistically with many chemicals and dusts jewelers have been exposed to, in some cases multiplying the risk of damage really dramatically. The materials, waxes, metals, investments we work with are all chemicals and can affect the body. The fumes that waxes produce during burnout are dangerous. Toxic metals like cadmium may be in older metal that is remelted. Heat causes chemical reactions to accelerate and sometimes starts them. Heat is definitely part of the casting process.

Physical: Burns, cuts, crushings, electrocution, other accidents, breathing in silica (silicosis), metal fumes, radiation (ultraviolet and infrared light can damage the eyes). Noise is not much of a hazard for casters, though torch sound and other shop noises can cause damage.

Ergonomic: Working heights, breaks in work, and repetitive movements have to be considered. Make sure that you do not have to be awkward at any point during the casting procedure or process, and if you’re doing it as a production system, then examine the ergonomic issues quite carefully.

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Fire: When working with gases, torch systems, hot metals, electric and gas kilns there is an increased chance of having a fire or an explosion. Gas handling and fire issues are of course, present with any torch use, and care and maintenance has to be had in regard to heating and melting with torches. Keep all flammable materials and liquids away from any source of heat or spark, make sure that you have fire extinguishers on hand, and that you have a fire plan.

The main dangers are breathing in cristobalite (silicosis hazard), dermatitis from repeated skin contact with investment, debubblizers, fluxes etc., breathing in metal fumes, hurting your eyes by not using the right kind of eye protection against chunks and light, burns and accidents with the electrical, gas and mechanical equipment used for casting.

The next section lists the hazards along with the procedure. As you read it you should understand that in the main, I consider the casting process to be very safe, that this is a discussion of the possibilities – and by no means will I have covered them all. That part of things is up to you as you consider safety in your own particular circumstances. Safety is your own responsibility.


Chemical: Specific chemicals include alkalis in investment, so that skin contact can foster dermatitis. There are detergents and de-fatting agents in debubblizers as well.

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Physical: Electrocution from electric short circuits, inhalation of cristobalite with the serious risk of silicosis (cristobalite is much more dangerous than ordinary silica), accidents due to tripping hazard or clutter in the workshop, investment splashed in the eyes. The main investments that jewelers use are up to sixty percent cristobalite.

Ergonomic: only a problem in real production situations, though working height and stance should be considered in any job.

Fire: electrical wiring problems. Always make sure the fusing is correct for the demands on it, and that you check and maintain wiring on any electrical device (such as a vibrator or vacuum investing machine).

Exposure Routes: eyes, inhalation (of cristobalite), skin

Safety Precautions to Use: Use local ventilation to suck the investment in the air away from where you are mixing and measuring it. Wear a mask when investing- though a mask is no substitute for local ventilation. Try to control dust. Mop floors and sponge surfaces with water to keep the dust down. Use latex or vinyl gloves to protect skin when touching the investment.

Substitution Options to Reduce Risk: McCann suggests replacing cristobalite with 30-mesh sand (Health Hazards 51); Richard Beckman’s article in Art Hazards News (v. 16.3 ) gives details on this procedure, and notes that “the particles in the 30 mesh sand…are too large to be airborne, and thus have a much lower chance of being inhaled” Beckman suggests one part investment plaster to one part sand, measured by weight, and claims that “the use of 30 mesh sand will in no way bring down the quality of surface reproduction as the plaster will flow around the grain size and give you the exact detail that was in your original wax.”. Rossol recommends using “non silica materials such as zircon when possible” (Rossol, 279). Outsourcing is an option.


Chemical: Specific chemicals include wax and plastic fumes from burnout. Fumes from a gas heat source. If using polyurethane or Styrofoam, instead of wax, for the positive mold, burnout can produce hydrogen cyanide and other toxic gases (McCann, Health Hazards 51-52). Styrofoam also produces carbon monoxide when burned (Rossol 277). Using foams in this way is not recommended. “When … waxes burn they release many toxic and irritating compounds including acrolein and formaldehyde. Acrolein is an exceedingly potent lung irritant, formaldehyde is a sensitizer and suspect carcinogen”. Burning organic chemicals like rosin, petroleum jelly, mineral oil and so on, added to wax, “will release carbon monoxide, and other toxic decomposition products” (Rossol 277).

Physical: Electrocution from short circuits (happened to me once in Germany reaching into a kiln), accident due to tripping hazard or clutter in the workshop. Burns while checking progress of burnout. Irritation from wax fumes and by-product. The rare possibility of investment popping and shooting into you when inspecting it.

Ergonomic: not much of an issue except for working heights, confined space issues and access to equipment.

Fire: electrical wiring or gas kiln types of fire hazards. If you open the kiln before the wax residue is gone a flare up can happen and billowing flames erupt – just close the door to put the fire out. See casting “Fire” section for more.

Safety Precautions to Use: You should have eye protection when near the flasks and wear protective gloves and clothing when handling them. Use gripping tongs that do not slip to move the flasks about during the burnout and to check them.

Substitution Options to Reduce Risk: Autoclaving can take care of some of the problems by removing the wax in a liquid form, and thus not converting the waxes into toxic fumes. Instead of using Styrofoam, consider wax as a safer alternative. Consider using waxes such as beeswax, which produce less toxic fumes than some of the plasticized waxes. One can always outsource.


Chemical: Specific chemicals include: borax, boric acid, possibly other casting fluxes like ammonium chloride or sodium chloride. Some people add a teensy smidgin of zinc to a melt a moment before casting to de-gas it. Some alloys may contain hazardous metals like cadmium, beryllium, arsenic, antimony and others. The torch flame is present as well during casting, with its chemical by-products. Metal fume fever causes flu-like symptoms: fever, chills, aches, usually 2-6 hours after exposure (Rossol 133) and lasts for 24 to 36 hours (McCann, Artist Beware! 425). Unless the metals are toxic, such as cadmium, those exposed seem to recover with no long-term effects. Be particularly wary of using non-precious scrap metal for casting, as it may contain metals that will produce toxic fumes when melted. Scrap and reclaimed mystery metals may also be coated with lead- or cadmium-based paints, which produce poisonous gases when heated. One is exposed to mineral oils and lubricants when working with machines.

Physical: Electrical hazards. If one is using an induction melting crucible, and electric kilns, then electrocution is a risk, as is fire. Accidents due to tripping hazard or clutter. Injuries in the form of mechanical parts cracking or smashing into a hand that is in the incorrect position or place. Burns while removing and preparing flasks for casting. Accidents with the casting machine through not having balanced it correctly or maintained and checked it properly before using it. Such an accident could result in a broken arm or red-hot metal globs spattering across the room. There is an explosion hazard if gas torches are used to heat during casting. Particles of investment dust, particularly present during centrifugal casting, can be breathed in and cause lung disease.

Ergonomic: Primarily this has to do with working heights, body positions, setting things up so you do not have to twist and turn your body when you are transferring things or checking on them. In a production situation, you would have to examine the workspace and the job very particularly to ensure that ergonomic issues are addressed.

Fire: You’re dealing with heat here, so this means either electrical equipment or gas kilns or torches as a heat source for melting. If electrical, then all issues of electrical safety have to be addressed, current draw, fusing, wire conditions, maintenance, and the possibility of electrocution. If gas, then all gas handling issues have to be addressed: maintenance checking for leaks, proper storage, proper usage of equipment, flashback arrestors, and so on and so forth.

Exposure Routes: Inhalation of wax fumes, and metal fumes, of dusts of various kinds, fumes from fluxes, and gas. Skin contact with fluxes and other materials used should be avoided. Accidents and burns are possible. Radiation-infra-red and ultra-violet, possibly sodium flare as well-can affect the eyes, and a suitable shade should be worn.

Safety Precautions to Use: Use local ventilation. You are dealing with hot objects, so the kiln and casting spot must be in a segregated, fireproof area, and all flammable materials and liquids must be separated from the kiln and hot materials and open flame. Fireproof walls should surround the kiln area. A burn kit and ice should be on hand in case you get burnt. Ensure that you have a fire plan available. The casting area should be damp-wiped frequently to remove cristobalite dust.

Good maintenance, good housekeeping, of all equipment including the torch systems. Good ventilation, eye protection, both from particles and from radiation (infra-red, ultra-violet, sodium flare), are particularly important when using an oxy-acetylene or oxy-propane torch system, which emits significant amounts of ultra-violet light. Heat-protective gloves, leather apron, steel-toed boots, metal splash covers over the lace area, so that spilled metal cannot enter in. Have a shield around the casting machine to keep metal splashes segregated. The old washtub around the centrifuge is a reasonable shield. Have a full knowledge of all materials used: the fluxes, metals and the chemicals involved, as well as their effects. Make sure that copper, for instance, does not contain any beryllium.

Substitution Options to Reduce Risk: Outsource. Switch to other types of manufacturing procedures, such as metal stamping, construction, milling, computer-aided design manufacture and so on. Attempts at substitute materials are possible: for instance, one can apparently make up a non-cristobalite, or lower-cristobalite investment for some casting purposes. One can try and use waxes that do not contain multiple chemicals. If using Styrofoam for burnout, or other plastics, one may consider wax as a substitute for them. Sand casting may substitute for investment casting. Autoclaving may substitute for at least part of the burnout procedure and is to be recommended as reducing the amount of wax fumes produced.

It is hoped that this glimpse at casting in terms of safety has been of interest.

  1. McCann, Michael. Artist Beware. Rev. ed. New York: Lyons and Burford, 1992.
  2. —. Health Hazards Manual for Artists. 4th rev. ed. New York: Lyons and Burford, 1994.
  3. Rossol, Monona. The Artist’s Complete Health and Safety Guide. 2nd ed. New York: Allworth Press, 1994.
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